Liquid crystal display devices ranging from a large display device such as a television receiver to a small display device such as a mobile phone have been spreading. From now on, products with higher added values will be needed and are being developed. In recent years, in view of increase in concern about global environment and improvement in convenience of mobile equipment, development of liquid crystal display devices with low power consumption has attracted attention.
Patent Document 1 discloses a structure of a liquid crystal display device where all data signal lines are electrically isolated from a data signal driver, which results in a high impedance state, in order to maintain constant potentials of data signal lines in an idle period during which all gate lines and all the signal lines are not selected. This structure allows reduction in power consumption of the liquid crystal display device.
Non-Patent Document 1 discloses a structure of a liquid crystal display device where refresh rates differ between the case of moving image display and the case of still image display for reduction in power consumption of the liquid crystal display device. Non-Patent Document 1 also discloses a structure where AC signals with the same phase are supplied to a signal line and a common electrode also in an idle period so that fluctuation in drain-common voltage can be prevented, in order to prevent perception of flickers due to the fluctuation in drain-common voltage, which is caused by switch of signals between the idle period and a scan period in the case of still image display.